Real time kinematic (RTK) global positioning system (GPS) technology has been integrated with precision farming methodology to provide highly accurate seeding, cultivating, planting and harvesting operations. RTK GPS systems are used to control fully or semi-autonomous vehicles in these operations.
With RTK GPS that includes a local portable base station, the GPS can locate the tractor on which a GPS antenna is mounted to within less than an inch. With this capability, the location of the tractor, and therefore the individual plants of the crop, can be recorded. The position information derived from the GPS receiver can be employed to automatically guide the tractor on a predefined working path. This is true particularly on flat terrain where orientation of the tractor and any vehicle towed by the tractor is parallel to the direction of travel. However, when the terrain has a significant side slope, the tractor and any towed vehicle will tend to “crab” or “side wind”, i.e., orienting the tractor and towed vehicle at an angle to the line of travel due to the tractor and towed vehicle sliding sideways due to the influence of gravity.
When slopes are in the range of 2% or greater, contour farming is more effective. With this technique, the tractor and towed equipment traverse perpendicular to the slope, slowing the effect of soil erosion caused by water run-off and thus substantially increasing crop yields. However, gravity pulls the towed vehicle off the path of the tractor and it is very important for both the tractor and towed vehicle to stay on course.
When the towed vehicle is not in alignment with the tractor, the angle between the orientation of the tractor and the orientation of the towed vehicle must be measured to be able to compensate for the towed vehicle being off the path of the tractor. If this condition remains uncompensated, the towed vehicle, such as a planter or fertilizer applicator, might not be in alignment with the rows of strip-tillage and not be able to plant seeds or apply fertilizers efficiently, or such as a harvester, might not be in alignment with the rows of crops and not be able to harvest the crop efficiently.
Also, the tractor must be angled slightly uphill to compensate for the pull of gravity and maintain the tractor on the desired working path perpendicular to the slope. Therefore, even if the implement is mounted on a self-propelled vehicle, the vehicle orientation with respect to the direction of vehicle travel must be determined and compensated for, so that the implement is in alignment with the rows of crops.
In order to guide the towed vehicle to track the desired path, some mechanical apparatus, such as hydraulically operated coulter systems, can be attached to the towed vehicle to make it capable of electronically steering itself. There are other means to accomplish this, for instance, by steering the towed vehicle's carrying wheels.
Additionally, in order to guide the towed vehicle automatically, one must know either the true position of the towed vehicle relative to the path to be followed or the location of the towed vehicle relative to the tractor. A system using a second GPS antenna and receiver on the towed vehicle has provided such information in prior systems. However, the use of a second GPS antenna and receiver is a very expensive solution.
The location of the towed vehicle relative to the tractor can be determined using an angular position sensing system. However, the orientation of the tractor must be known to determine the location of the towed vehicle relative to the GPS antenna mounted on the tractor. The orientation of the tractor has been determined by using two GPS antennas and receivers fixed to the tractor. However, this again, is a very expensive solution.